The present invention relates to polymeric surface coatings and more particularly a method for identifying defects in wet polymeric surface coatings.
The process of applying polymeric surface coatings, such as automotive paints, to a surface is an important component in many manufacturing processes for both aesthetic and practical reasons. Polymeric coatings protect surfaces from degradation associated with physical conditions, such as light exposure or weather, while adding pleasing color or luster to visible surfaces.
Polymeric surface coatings can be applied in many different manners, including among others dipping, electrodeposition, and spraying. For most automotive applications, polymeric surface coatings are applied by spraying, with the coating being xe2x80x9ccuredxe2x80x9d, typically in an oven, in order to crosslink or harden the polymer components.
Application of polymeric surface coatings to surfaces is an inexact science. Defects in the coating caused by the application process are very common. Major defects can lead to premature coating failure, while minor defects may be unpleasing to the eye. Many of these defects are correctable by adjustments to application techniques, varying the composition of the coating or solvent delivery system, or adjusting the curing time or temperature. In this regard, it is important to discover the reasons why the defects are occurring in order to correct them as quickly as possible.
Many techniques are typically used to inspect surface coatings, from simple visual inspection to sophisticated surface measuring techniques. What is common among most of these techniques currently used is that they inspect dry, or cured, surface coatings. For example, U.S. Pat. No. 5,726,705 discloses an apparatus and method for inspecting defects or abnormalities of film by using a digitizing camera and light source.
One problem with inspecting cured coatings is determining where the problem causing the defect occurred. For instance, the problem could be caused by the spray equipment, the composition of the coating, or in the curing process. Another problem with inspecting cured coatings is that by the time the surface is inspected, a number of other parts may have already been coated with similar defects, and the cost to reapply or touch-up the surfaces is magnified by the number of parts that has been coated before the discovery of t he reason for the defect. For a production line for automobiles, for example, the number of units that could be affected may approach 100 units or more.
Thus, it is highly desirable to discover a defect in the wet surface coating at the earliest possible instance, as it limits the number of possible root causes of the surface defect, and further because it decreases the costs associated with reapplication or touching-up of parts by limiting the number of parts having the defect. This early discovery has the added benefit that any problems associated with curing will be limited to the curing mechanism or process, or due to the coating composition, and not due to the application of the coating. Another benefit of early discovery is that the sequencing of parts may be altered or adjusted to spray parts not being affected by the occurring defect. For example, if an automotive assembly line is having problems with red basecoats or with a particular paint bell atomizer, the assembly line may be sequenced to spray other colors or use other spray equipment until the root cause of the problem is remedied.
It is thus an object of the present invention to provide an apparatus and method for inspecting a wet (uncured) polymeric surface coating immediately after application so as to instantaneously observe defects, thus limiting or eliminating costs associated with retouch or reapplication.
The above object is accomplished by either digitizing an image in one of four vision systems (Specular Imaging, Directional Imaging, Patterned Imaging, or Diffused Light Imaging) of the wet polymeric surface with a digital camera or by scanning a polymeric surface with a laser sensor and scanner and comparing the produced images with known standards that indicate failures or passing surfaces.
One preferred method for visually inspecting a polymeric surface coating for defects or abnormalities comprises the steps of: capturing an image of the wet polymeric surface coating with a vision system and a detector system; digitizing the image; comparing the digitized image to a reference digitized image; and notifying the operator is the digitized image is a passing image or failing image due to a surface defect or abnormality.
Other objects and advantages of the present invention will become apparent upon considering the following detailed description and appended claims, and upon reference to the accompanying drawings.